Examples include a project’s scope, which could contain information about the current project such as
the project file’s location. QgsExpressionContextScope can encapsulate both variables (static values)
and functions(which are calculated only when an expression is evaluated).

See QgsExpressionContextUtils for helper methods for working with QgsExpressionContextScope objects.

Convenience method for setting a variable in the context scope by name name and value. If a variable
with the same name is already set then its value is overwritten, otherwise a new variable is added to the scope.
If the isStatic parameter is set to true, this variable can be cached during the execution
of QgsExpression.prepare()